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           #include <sys/types.h>
           #include <db.h>


           Note  well:  This  page documents interfaces provided in glibc up until
           version 2.1.  Since version 2.2, glibc no longer provides these  inter-
           faces.   Probably,  you  are looking for the APIs provided by the libdb
           library instead.
           The routine dbopen(3) is the library interface to database files.   One
           of  the supported file formats is btree files.  The general description
           of the database access  methods  is  in  dbopen(3),  this  manual  page
           describes only the btree-specific information.
           The  btree  data structure is a sorted, balanced tree structure storing
           associated key/data pairs.
           The btree access-method-specific data structure provided  to  dbopen(3)
           is defined in the <db.h> include file as follows:
               typedef struct {
                   unsigned long flags;
                   unsigned int  cachesize;
                   int           maxkeypage;
                   int           minkeypage;
                   unsigned int  psize;
                   int         (*compare)(const DBT *key1, const DBT *key2);
                   size_t      (*prefix)(const DBT *key1, const DBT *key2);
                   int           lorder;
               } BTREEINFO;
           The elements of this structure are as follows:
           flags  The  flag  value is specified by ORing any of the following val-
                  R_DUP  Permit duplicate keys in the tree, that is, permit inser-
                         tion  if  the  key  to  be inserted already exists in the
                         tree.  The default behavior, as described  in  dbopen(3),
                         is  to  overwrite a matching key when inserting a new key
                         or to fail if the R_NOOVERWRITE flag is  specified.   The
                         R_DUP  flag  is overridden by the R_NOOVERWRITE flag, and
                         if the  R_NOOVERWRITE  flag  is  specified,  attempts  to
                         insert duplicate keys into the tree will fail.
                         If  the  database  contains  duplicate keys, the order of
                         retrieval of key/data pairs is undefined if the get  rou-
                         tine  is used, however, seq routine calls with the R_CUR-
                         SOR flag set will always return the  logical  "first"  of
                         any group of duplicate keys.
                  The  maximum  number  of keys which will be stored on any single
                  page.  Not currently implemented.
                  The minimum number of keys which will be stored  on  any  single
                  page.  This value is used to determine which keys will be stored
                  on overflow pages, that is, if a key or data item is longer than
                  the  pagesize divided by the minkeypage value, it will be stored
                  on overflow pages instead of in the page itself.  If  minkeypage
                  is  0  (no  minimum number of keys is specified) a value of 2 is
           psize  Page size is the size (in bytes) of the pages used for nodes  in
                  the  tree.   The  minimum page size is 512 bytes and the maximum
                  page size is 64K.  If psize is 0 (no page size is  specified)  a
                  page size is chosen based on the underlying filesystem I/O block
                  Compare is the key comparison function.  It must return an inte-
                  ger  less  than, equal to, or greater than zero if the first key
                  argument is considered to be respectively less than,  equal  to,
                  or  greater  than  the second key argument.  The same comparison
                  function must be used on a given tree every time it  is  opened.
                  If  compare  is  NULL (no comparison function is specified), the
                  keys are compared lexically, with shorter keys  considered  less
                  than longer keys.
           prefix Prefix  is  the  prefix comparison function.  If specified, this
                  routine must return the number of bytes of the second key  argu-
                  ment  which  are  necessary to determine that it is greater than
                  the first key argument.  If the keys are equal, the  key  length
                  should  be  returned.   Note,  the usefulness of this routine is
                  very data-dependent, but, in some data sets can produce signifi-
                  cantly  reduced  tree sizes and search times.  If prefix is NULL
                  (no prefix function is specified), and no comparison function is
                  specified,  a  default  lexical  comparison routine is used.  If
                  prefix is NULL and a comparison routine is specified, no  prefix
                  comparison is done.
           lorder The  byte  order  for  integers in the stored database metadata.
                  The number should represent the order as an integer;  for  exam-
                  ple, big endian order would be the number 4,321.  If lorder is 0
                  (no order is specified) the current host order is used.
           If the file already exists (and the O_TRUNC flag is not specified), the
           values  specified for the arguments flags, lorder and psize are ignored
           in favor of the values used when the tree was created.
           Forward sequential scans of a tree are from the least key to the great-
           errors specified for the library routine dbopen(3).


           Only big and little endian byte order is supported.


           dbopen(3), hash(3), mpool(3), recno(3)
           The Ubiquitous B-tree, Douglas Comer, ACM Comput.  Surv.  11,  2  (June
           1979), 121-138.
           Prefix  B-trees, Bayer and Unterauer, ACM Transactions on Database Sys-
           tems, Vol. 2, 1 (March 1977), 11-26.
           The Art of Computer Programming Vol. 3:  Sorting  and  Searching,  D.E.
           Knuth, 1968, pp 471-480.
                                      2012-04-23                          BTREE(3)

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